A. Field of the Invention
The present invention relates to a security element for a security paper, value document or the like, to a value document having such a security element, and to a method for manufacturing such a security element.
B. Related Art
Objects to be protected are frequently equipped with a security element which permits verification of the authenticity of the object and at the same time serves as protection from unauthorized reproduction.
Objects to be protected are for example security papers, identity documents and value documents (such as e.g. bank notes, chip cards, passports, identification cards, identity cards, shares, investment securities, deeds, vouchers, checks, admission tickets, credit cards, health cards, etc.) as well as product authentication elements, such as e.g. labels, seals, packages, etc.
For such a security element it is known to employ optically variable security inks as are described e.g. in EP 0 227 423 A2. Such security inks contain platelet-shaped pigments with a thin-film interference coating, so that for a viewer the color of the individual pigments depends on the viewing angle. The security inks with the described platelet-shaped pigments can be printed on a bank note such that the pigments are aligned approximately parallel to the surface of the bank note, and the printed area changes its color in accordance with the thin-film coating of the pigments upon tilting of the bank note.
It is further known to provide such pigments with an additional magnetic layer (U.S. Pat. No. 4,838,648), so that the pigments can then be aligned by means of suitable magnets and fixed (U.S. Pat. No. 7,517,578 B2). This makes it possible for the pigments to be aligned parallel to each other substantially more precisely, on the one hand, which leads to a considerably higher chroma (=more brilliant colors). On the other hand, it provides the possibility of orienting the pigments not only parallel to the substrate surface, but in principle in any direction. In particular, the pigments of different regions of the security element can also be aligned in different directions. Depending on the magnet assembly used, there can be achieved between the differently oriented regions relatively abrupt as well as gentle transitions.
From JP 2008-80609 A there is known a further method for aligning the platelet-shaped pigments wherein the security ink with the pigments is so applied to an embossed relief structure that the pigments are aligned approximately parallel to the relief. By suitable design of the relief there can be realized regions with differently oriented pigments and accordingly different colors.
The described optically variable security inks are relatively expensive, on the one hand. On the other hand, the alignment of the pigments via magnets is of course limited, because the magnetic fields necessary for alignment cannot be arbitrarily formed. Further, the security elements cannot be especially finely resolved, which is due to the usually employed screen printing processes, on the one hand, and to the transitions of the necessary magnetic fields not being arbitrarily sharp, on the other hand.
Besides the color change, the security inks also frequently lead to a glitter effect similar to metallic lacquering on automobiles.